1. Field of the Invention
The present invention relates to an adhesive composition.
2. Description of the Related Art
In general, a liquid crystal display device (LCD') has a liquid crystal panel including liquid crystal cells and at least two polarizing plates laminated to both sides of each liquid crystal cell.
The polarizing plate typically consists of an iodine-based polyvinyl alcohol polarizer and a protective film to protect both sides of the polarizer, and is combined with the liquid crystal cell through an adhesive (layer).
Such adhesive used to combine the polarizer with the liquid crystal cell must possess both durability such as heat resistance, heat/moisture resistance, etc., and re-workability. However, since characteristics of the adhesive to achieve such physical properties substantially oppose each other, these physical properties still have yet to be mutually satisfied.
In order to solve conventional problems described above, Japanese Patent Laid-Open Publication No. H10-044291 discloses use of an acrylic polymer having specific functional groups, as an adhesive resin. However, this method causes increase in adhesive strength at elevated temperature, thus having difficulty in attaining desired re-workability. Korean Patent Laid-Open Publication No. 2009-0055481 discloses a copolymer based on a monomer having 1 to 16 alkyl groups as well as a hydroxyl group-containing monomer, and an adhesive composition including styrene resin cross-linked to the copolymer.
Meanwhile, a process for combination of a polarizing plate with a liquid crystal cell may generate electrostatic discharge during peeling of a release film. Such electrostatic discharge may cause various problems including, for example: surface contamination of an optical part due to impurity adsorption; stains caused by distortion of liquid crystal orientation; damage of thin film transistor (TFT) circuits, or the like. Therefore, conventional methods generally adopt an addition of ionic compounds to an adhesive as an anti-static agent.
However, the anti-static agent based on ionic compounds moves toward a surface of the adhesive composition, in turn creating problems caused by decreased durability, such as bubbling on a bonded face between an adhesive layer and a liquid crystal cell, delamination, etc. Also, ionic compounds often inhibit gelling of the adhesive, to thereby entail difficulties in controlling, i.e., decreasing a curing period of the adhesive.